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Update:August 22, 2017

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Tropical forests have colorful squirrel species that can be distinguished based on fur color


Article title

(1) Colour vision in Finlayson’s squirrel (Callosciurus finlaysonii): Is conspicuous pelage colour useful for species recognition ?

(2) Colour polymorphism and genetic relationships among twelve subspecies of Callosciurus finlaysonii in Thailand

Author (affiliation)

(1) Noriko Tamura (a), Yukiko Fujii(b), Phadet Boonkhaw(c), Umphornpimon Prayoon (c), Budsabong Kanchanasaka (c)

(2) Phadet Boonkhaw (c), Umphornpimon Prayoon (c), Budsabong Kanchanasaka (c), Fumio Hayashi (d), Noriko Tamura (a)

 (a) Tama Forest Science Garden, FFPRI, Hachioji, Tokyo, Japan.

 (b) Nature Study and Squirrel Research, Yokohama, Kanagawa, Japan.

 (c) Department of National Park Wildlife and Plant Conservation, Bangkok, Thailand.

 (d) Tokyo Metropolitan University, Hachioji, Tokyo, Japan.

Publication Journal

(1) Tropical Zoology, 30(3):110-124, July 2017, DOI: 10.1080/03946975.2017.1345471( External link )

(2) Mammalian Biology, 85:6-13, July 2017, DOI: 10.1016/j.mambio.2017.02.001( External link )

Content introduction

Forests in Southeast Asia have an extremely high biodiversity, for example, the highest diversity of squirrel species is distributed in the world. However, genetic relationships and coexistence mechanisms among these species have not been adequately studied. In this study, we experimentally and genetically examined how these closely related species inhabiting the same parts of forests can be distinguished and show reproductive characteristics distinct from one another. Finlayson’s squirrels (Callosciurus finlaysonii), as the targets of our study, show conspicuous fur colors, including black, white, and red. The closely related brown Pallas’s squirrels (C. erythraeus) and orange golden-backed squirrels (C. caniceps) also inhabit the same area. Thus, we conducted a learning experiment wherein we prepared the experimental papers with the same color characteristics as the squirrel’s fur colors (five colors: black, white, red, orange, and brown) and fed squirrels as a reward for distinguishing a correct color.

Results showed that squirrels distinguished black, red, and white from orange, and black and white, but not red, from brown. This is associated with squirrels’ dichromatic vision (Note), suggesting that white, black, and orange were effective in recognition of the same species. Second, we examined genetic relationships, which showed that orange golden-backed squirrels evidently divided into a different group, whereas brown Pallas’s squirrels (G4 in the figure) and the colorful Finlayson’s squirrels, previously considered to be different species, could not be clearly distinguished from one another. These squirrels are believed to be divided into seven groups based on major rivers and the sea. Although it would appear that the conspicuous fur colors are characteristics acquired by chance through being geographically isolated, the colors may aid the recognition of the same species and promote species differentiation in tropical forests, wherein a variety of closely related species coexist or live close to one another.

(Note) Dichromatic vision means peak sensitivities at two different wavelengths. Humans and most monkeys with peak sensitivities at three different wavelengths have trichromatic vision. Red and green, which are recognized with trichromatic vision, are difficult to distinguish with dichromatic vision.



Figure:Tropical forests have colorful squirrel species that can 


Figure. Fur color polymorphism and genetic groups among Finlayson's squirrels and Pallas's squirrels in Thailand. [genetically divided into seven groups (G1-G7) based on rivers (shown with dashed lines) and the sea]